1. Field of the Invention
The present invention relates to a driving environment surveillance apparatus for detecting obstacle in front of a running vehicle to inform a driver for easily recognizing the presence of the obstacles.
2. Description of the Prior Art
Conventionally, as the technologies of this kind, there are known an active type one (disclosed in Japanese Patent Publication (Kokoku) No. 60-4011 and so forth) in which a microwave or infrared laser light is transmitted and the reflected signal from obstacles and so forth is received to detect the distance between vehicles, the presence of the obstacles, the relative distance, the relative speed, and so forth, and a passive type one (disclosed in Japanese Patent Publication (Kokoku) No. 63-38085, Japanese Patent Publication (Kokoku) No. 63-46363, Japanese Patent Publication (Kokai) No. 63-52300, and so forth) in which an image sensor is used to catch an object in front of the vehicle as an image data and so as to detect an obstacle (including another vehicle) by means of image processing, whereby the distance to the obstacle is detected based on the principle of the triangulation by two sets of optical system. Both of these conventional technologies, although the systems are different to each other, detect the presence or absence of an obstacle on the front periphery of the running own vehicle, the relative distance to the obstacle, and the relative speed, to output the distance data or the speed data to the driver of the own vehicle.
FIG. 1 is a plan view showing a conventional driving environment surveillance apparatus disclosed in, for example, the Japanese Patent Publication (Kokoku) No. 61-6349. In the drawing, reference numeral 1 is a vehicle equipped with a laser radar 4, 2 is an obstacle (for example, a vehicle stopping on a side of a road) which is present on the left side in a travelling direction of the vehicle 1, and 3 is another obstacle (for example, a post box) which is present on the right side in the travelling direction of the vehicle 1.
Also, reference numeral 4 means the laser radar which is provided in the most-front of the vehicle 1 to emit a light beam 6 so as to scan in the range of -10.degree.&lt;.theta.&lt;+10.degree. with respect to a center point of the front-end of the vehicle. In the laser radar 4, a scanning interval .DELTA..theta. (i.e., an interval between adjacent light beams 6) is set at 0.1.degree..
A description will now be given of the operation.
When the laser radar 4 emits the light beam 6 sequentially starting from the most left end (N=0) toward the right side, the light beams 6 from N=g to N=i return to the vehicle 1 as reflected lights due to the presence of the obstacle 2, and the laser radar 4 receives the reflected lights. In this connection, the laser radar 4 can not receive the light beam 6 for N=i+1 because of reflection by a side surface of the obstacle 2.
Here, it is assumed that P.sub.1 means a reflection point of the light beam 6 at the most right end (N=i) whose reflected light from the obstacle 2 can be received by the laser radar 4. Accordingly, a distance QP.sub.1 can be detected as QP.sub.1 =R.sub.1 based upon a reflection time, and a distance P.sub.1 P.sub.3 (=y.sub.1) from P.sub.1 to the center line (the z-axis) of the vehicle can be expressed as follows: EQU P.sub.1 P.sub.3 =y.sub.1 .apprxeq.R.sub.1 .multidot..theta..sub.i ( 1)
where .theta..sub.i means a deflection angle of the light beam 6 for N=i (the deflection angle 8.sub.i being a known number for the laser radar 4). Further, it is assumed that P.sub.2 means a reflection point of the light beam 6 at the most left end (N=g) whose reflected light from the obstacle 2 can be received by the laser radar 4. Thereby, it is similarly possible to detect a distance QP.sub.2 as QP.sub.2 =R.sub.2 based upon the reflection time. A distance P.sub.2 P.sub.4 (=y.sub.2) from the point P.sub.2 to the center line (the z-axis) of the vehicle can be expressed as follows: EQU P.sub.2 P.sub.4 =y.sub.2 .apprxeq.R.sub.2..theta..sub.g ( 2)
where .theta..sub.g means a deflection angle of the light beam 6 for N=g (the deflection angle .theta..sub.g being a known number for the laser radar 4). Accordingly, the recognition of the positions P.sub.1 and P.sub.2 enables recognition of the relative distance or the azimuth from the vehicle 1 to the obstacle 2.
Detection of the obstacle 3 is identical with that of the obstacle 2, and a description thereof is omitted.
Since a detecting method in a height direction of the obstacles 2 and 3 is identical with that in the horizontal direction in principle, a description thereof is also omitted. In this connection, FIG. 2 shows the light beam 6 emitted from the laser radar 4 to extend in the height direction.
The conventional driving environment surveillance apparatus is constructed as set forth above. Therefore, it is necessary to provide a fine interval .DELTA..theta. between the light beams 6 emitted from the laser radar 4 in order to detect the relative distance or the azimuth from the vehicle 1 to the obstacles 2 and 3 with high accuracy. However, as the interval .DELTA..theta. between the light beams 6 becomes more fine, a longer time is required for detecting the obstacles 2 and 3. As a result, there are problems in that, for example, real-time detected data of the obstacles 2 and 3 can not be provided, and the conventional apparatus is not practical for the vehicle in a running condition.